U.S. patent application number 11/116970 was filed with the patent office on 2006-05-04 for methods and apparatus for sensing cardiac activity via neurological stimulation therapy system or medical electrical lead.
Invention is credited to Michael R.S. Hill, Gary W. King, Steve R. Laporte, Thomas J. Mullen, Xiaohong Zhou.
Application Number | 20060095081 11/116970 |
Document ID | / |
Family ID | 35825453 |
Filed Date | 2006-05-04 |
United States Patent
Application |
20060095081 |
Kind Code |
A1 |
Zhou; Xiaohong ; et
al. |
May 4, 2006 |
Methods and apparatus for sensing cardiac activity via neurological
stimulation therapy system or medical electrical lead
Abstract
According to the present invention at least a pair of
neurological stimulation electrodes are disposed in, on, about,
adjacent and/or within excitable neural tissue of a subject.
Cardiac activity of a patient is detected using one or more
electrodes adapted for delivery of a neurological stimulation
therapy (NST). Following detection of certain types of cardiac
activity one or more of the plurality of stimulation electrodes
deliver or withhold NST, if desired in synchrony with the cardiac
activity or in response to the detected cardiac activity. The NST
delivered includes without limitation subcutaneous stimulation,
peripheral, TENS and/or vagal nerve stimulation therapy or the
like.
Inventors: |
Zhou; Xiaohong; (Plymouth,
MN) ; Mullen; Thomas J.; (Andover, MN) ; Hill;
Michael R.S.; (Minneapolis, MN) ; Laporte; Steve
R.; (Rhinelander, WI) ; King; Gary W.;
(Fridley, MN) |
Correspondence
Address: |
MEDTRONIC, INC.
710 MEDTRONIC PARK
MINNEAPOLIS
MN
55432-9924
US
|
Family ID: |
35825453 |
Appl. No.: |
11/116970 |
Filed: |
April 28, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60623493 |
Oct 29, 2004 |
|
|
|
Current U.S.
Class: |
607/2 |
Current CPC
Class: |
A61N 1/36114 20130101;
A61N 1/36135 20130101; A61N 1/0551 20130101 |
Class at
Publication: |
607/002 |
International
Class: |
A61N 1/18 20060101
A61N001/18 |
Claims
1. A method for monitoring cardiac activity or cardiac condition,
comprising the steps of: placing a plurality of electrodes adapted
to serve as a source of electrical neurological stimulation
adjacent to, on or within a portion of neurological tissue of a
patient; and sensing cardiac activity using operative circuitry
coupled to at least one of said plurality of electrodes.
2. A method according to claim 1, wherein at least one of the
plurality of electrodes comprises a unipolar electrode, and said
unipolar electrode electrically communicates with an electrically
conductive portion of a medical device canister.
3. A method according to claim 1, further comprising filtering the
sensed cardiac activity.
4. A method according to claim 2, wherein the portion of the
medical device canister retains a surface-type electrode.
5. A method according to claim 1, wherein at least two of the
plurality of electrodes comprises a pair of electrically bipolar
electrodes.
6. A method according to claim 1, further comprising coordinating
the delivery of neurological therapy via at least one of the
plurality of electrodes with at least a part of the sensed cardiac
activity.
7. A method according to claim 1, further comprising delivering a
neurological therapy via at least one of the plurality of
electrodes to one of a portion of the vagus nerve and a portion of
the spinal cord of a patient.
8. A method according to claim 1, further comprising: applying an
electrical therapy via at least one of the plurality of
electrode(s).
9. A method according to claim 8, wherein said therapy is applied
to a one of: the spinal cord, a portion of a vagus nerve, a ganglia
portion of a vagus nerve, a portion of myocardium, a peripheral
nerve, a portion of subcutaneous nerves tissue
10. A method according to claim 1, wherein the operative circuitry
and the plurality of electrodes are one of disposed external to a
patient and in at least partial contact with the patient.
11. A method according to claim 1, further comprising: signaling
one of the subject and a clinician regarding a status or change in
the sensed cardiac activity.
12. A method according to claim 11, wherein the signaling step
comprises at least one of: signaling via an auditory signal,
signaling via a vibratory signal, signaling via a visual signal,
signaling via a radio frequency signal, signaling via an
electromagnetic signal.
13. A method according to claim 12, wherein the signaling step
occurs at least in part in response to one of: onset of a detected
arrhythmia, termination of a detected arrhythmia, a detected
episode of acute myocardial ischemia, a detected relatively stable
heart rate, a detected relatively accelerating heart rate, a
detected relatively slowing heart rate, an episode of heart rate
variability, a T-wave abnormality condition, a T-wave alternans
condition.
14. A method according to claim 13, further comprising: means for
delivering spinal cord stimulation therapy coupled to said
plurality of electrodes, said means for delivering operating
automatically in response to the initiation of the signaling step
wherein said initiation occurs due to one of: the detected episode
of acute myocardial ischemia, the detected relatively accelerating
heart rate, the T-wave abnormality condition, the T-wave alternans
condition.
15. A method according to claim 14, further comprising ceasing the
spinal cord stimulation therapy delivery upon one of expiration of
a predetermined temporal interval and termination of an episode of
non-typical cardiac activity or an event of non-typical cardiac
activity.
16. A method according to claim 14, further comprising ceasing the
signaling upon one of expiration of a predetermined temporal
interval and termination of an episode of non-typical cardiac
activity or an event of non-typical cardiac activity.
17. A method according to claim 13, further comprising means for
delivering spinal cord stimulation coupled to said plurality of
electrodes in response to a change in the monitored cardiac
activity.
18. A device for monitoring cardiac conditions, comprising: a
plurality of electrodes adapted to be implanted adjacent to or
within a portion of a spinal cord of a subject; and means for
performing a selection of two or more of said electrodes for
sensing an electrical signal originating from a heart of said
patient.
19. A device according to claim 18, further comprising a memory
structure for storing the electrical signal.
20. A device according to claim 19, further comprising: means for
wirelessly transmitting coupled to the means for performing
selection said means adapted to transmit at least one of the
electrical signal and the stored electrical signal.
21. A device according to claim 18, further comprising: a signaling
device adapted to alert the subject or a clinician, said signaling
device coupled to the means for selection.
22. A device according to claim 21, wherein the signaling device
comprises at least one of: an auditory signal, a vibratory signal,
a visual signal, a radio frequency signal, an electromagnetic
signal.
23. A device according to claim 22, wherein the signaling device is
energized in response to one of: a detected arrhythmia, a detected
terminated arrhythmia, a detected episode of acute myocardial
ischemia, a detected relatively stable heart rate, a detected
relatively accelerating heart rate, a detected relatively slowing
heart rate, an episode of heart rate variability, a T-wave
abnormality, a T-wave alternans condition.
24. A device according to claim 23, wherein said detected episode
of acute myocardial ischemia comprises at least two monitored
cardiac cycles in which an S-T segment magnitude of the subject's
PQRST complex is one of elevated and depressed from a baseline S-T
segment magnitude.
25. A device according to claim 22, further comprising a band-pass
filter operatively coupled to an automatic gain control amplifier
and at least one of the plurality of electrodes.
26. A device for monitoring cardiac conditions from a location
proximate or within a portion of the spinal cord of a subject,
comprising: a plurality of electrodes adapted to be implanted
adjacent to or within a portion of a spinal cord of a subject, said
electrodes designed to deliver electrical stimulation a portion of
a spine of a patient; and a processor means for performing a
selection of two or more of said plurality of electrodes for
sensing an electrical signal originating from a heart of said
patient.
Description
STATEMENT OF PRIORITY AND INCORPORATION BY REFERENCE
[0001] This non-provisional U.S. patent application hereby claims
the benefit of prior U.S. provisional patent application Ser. No.
60/623,493 which was filed 20 Oct. 2004 and is entitled, "METHOD
AND APPARATUS FOR DETECTING CARDIAC ACTIVITY VIA AT LEAST ONE
ELECTRODE DISPOSED IN OR ADJACENT TO THE SPINAL COLUMN" the
contents of which are incorporated by reference herein as if fully
set forth in the body of the instant document.
FIELD OF THE INVENTION
[0002] This invention relates to apparatus and methods for sensing
cardiac activity electrical signals and for optionally providing
electrical neurological stimulation therapy at one or more neural
sites using one or more neurological stimulation electrodes
operatively coupled to excitable neural tissue of a subject (e.g.,
in or adjacent to the spinal column and spaced from the
myocardium).
BACKGROUND OF THE INVENTION
[0003] Various extant electrical therapies for a variety of cardiac
and neurological disorders operate by delivering electrical
stimulation to a portion of myocardium, a spinal cord, a part of
the vagus nerve bundle, and/or other nerve fibers that affect a
bodily function and/or an organ of the body, etc. Typically, nerve
stimulation therapy was manually initiated or triggered by a
patient when the patient becomes symptomatic. Depending on the
location of neurological stimulation therapy delivery, remote
monitoring of an affected organ can increase the complexity of an
implantable therapeutic apparatus and/or the risk to a patient from
various complications.
[0004] A need exists in the art for so-called closed loop
neurological therapy delivery, including therapeutic neurological
stimulation based at least in part on the monitoring of an affected
organ that is located remotely from the site or sites of
neurological therapy.
SUMMARY OF THE INVENTION
[0005] Systems and methods according to the invention provide for
remote monitoring of the condition or functioning of a subject's
organ (e.g., cardiac activity signals from a location spaced from
the heart) using one or more electrodes adapted to deliver
neurological therapy positioned in electrical communication with
excitable neural tissue of a subject (e.g., in, on, or near
excitable neural tissue).
[0006] The electrodes may comprise one or more skin-based
electrodes as well as subcutaneous and/or submuscular electrodes
that are operatively electrically coupled to excitable spinal cord
tissue from a location on, in or near the spinal cord, or near
other excitable neural tissue. The system further includes a
controller coupled to the electrodes for processing the physiologic
signal from the monitored organ and delivering neurological therapy
on demand or as dictated by a neurological therapy delivery
algorithm. The controller may be external to an internal site or
sites of neurological therapy delivery, subcutaneously placed, or
fully implanted within a patient's body. The system may
additionally include a variety of optional electrodes and medical
devices (e.g., drug delivery pumps) but in an exemplary embodiment
is devoid of transvenous and/or endocardial sensors and other
components. The optional electrodes or devices may be partly or
wholly externally located, subcutaneously placed, or fully
implanted. Any component of the system may be electrically
connected to any other component through conductive leads or wires,
or in wireless communication with any other component. The system
is adapted to remotely monitor physiologic conditions of an organ
using sensing vectors defined by a pair of the neurological therapy
delivery electrodes or by a single electrode electrically coupled
to a conductive portion of a housing for the controller.
Neurological stimulation therapy or other therapy is initiated and
modulated based on the time-varying physiological condition of said
organ, due at least in part to the fact that the organ is directly
or indirectly affected by the neurological stimulation.
[0007] The present invention also includes computer readable media
for storing instructions that cause a processor-controlled
apparatus to execute the methods of the invention. The media
includes all media now known or later developed including
magnetically-encoded media, optically-encoded media, FLASH and
programmable logic circuits and arrays and the like including
equivalents thereof.
[0008] A current spinal cord stimulation (SCS) device used for
angina pectoris uses an open-loop mode for stimulation. In
contrast, in one embodiment the present invention includes a
modified SCS device operating as a closed-loop device so that the
therapy can be timely applied once myocardial ischemia or other
cardiac dysfunction is detected remotely using the SCS electrodes.
Thus, the invention helps improve the efficacy of a neurological
stimulator and at the same time increase service life or longevity
of the device due to only delivering neurological stimulation at
certain times and/or in response to detected cardiac condition
(e.g., ischemia, heart rate variability, high or low heart rate,
etc.) and/or withholding neurological stimulation in response to
cardiac activity or condition. In another embodiment of the
invention, neurological stimulation therapy electrodes adapted to
couple to the vagus nerve are employed to remotely monitor cardiac
conditions. Herein such neurological stimulation shall be referred
to from time to time as Neurological Stimulation Therapy (NST)
which shall comprehend all forms of electrical therapy directed to
a portion of the nervous system of a subject.
[0009] A specific advantage is to improve ischemia detection,
especially to improve detection of posterior myocardial ischemia
and infarction. In addition, the cardiac signal recorded by a
neurological lead and device can be used for detection of cardiac
arrhythmias and monitoring of Q-T intervals, T-wave changes (e.g.,
alternans) as well as autonomic indicators such as heart rate
variability and heart rate turbulence. Importantly, the invention
does not require an intracardiac lead for monitoring cardiac
activity. Therefore, a closed-loop neural stimulation can be
achieved with the information from cardiac electrical signals. By
example and without limitation the following features of the
invention summarize certain aspects of the invention: (1)
neurological stimulation-type medical electrical leads with
capability for cardiac sensing; (2) neural stimulation device with
capability of cardiac sensing; (3) algorithm for filtering
artifacts due to neurological stimulation device and/or
myopotentials due to patient activity; and (4) delivery of
neurostimulation synchronized with cardiac electrical or mechanical
cycles.
[0010] In still another aspect of the instant invention, methods
are provided. Certain methods comprise providing at least one NST
electrode in a region associated with excitable nervous tissue of a
patient and applying electrical stimulation via the at least one
NST electrode to alter the functioning of a patient's heart. One or
more predetermined physiologic cardiac parameters of the patient
are remotely monitored via the NST electrodes, and the electrical
stimulation is adjusted based on the one or more predetermined
physiologic parameters.
[0011] In another embodiment, an apparatus is provided comprising
at least one electrode that may be positioned in a region
associated with central nervous tissue of a patient. Structural
means for controlling the delivery of NST delivery to alter
functioning of a patient's heart is also provided. The controlling
means utilizes one or more predetermined cardiac parameters of the
patient, and the electrical stimulation is adjusted based on the
one or more predetermined parameters.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The present invention is described and depicted herein using
a limited set of drawings wherein like components are referred to
by like reference numerals and the drawings are not drawn to scale
nor intended to illustrate any unrelated components or ancillary
method steps. Those of skill in the art to which the invention is
directed will appreciate insubstantial modifications or changes to
the invention each of which is intended to be expressly covered
hereby.
[0013] FIG. 1A illustrates a stylized representation of a posterior
view of a patient with electrodes positioned thereon.
[0014] FIG. 1B is a diagram illustrating an implantable stimulation
device implanted within a patient.
[0015] FIG. 2 illustrates a stylized block diagram of a controller
of FIG. 1.
[0016] FIG. 3 illustrates a stylized flowchart of a control routine
that may be performed by the controller of FIGS. 1 and 2.
[0017] FIG. 4 is a flowchart illustrating one embodiment of the
current invention.
[0018] FIG. 5 is a flowchart illustrating one embodiment of
concomitant therapy delivery that may be provided in conjunction
with neural stimulation.
[0019] FIG. 6 is a schematic depiction of a neurological
implantable pulse generator (IPG) coupled to a multi-electrode
neurological medical electrical lead.
[0020] FIG. 7 is a temporal trace of cardiac activity signals
collected using SCS electrodes spaced from a canine heart and
clearly depicts the deflections of the cardiac cycle.
[0021] FIGS. 8A-C depict three temporal tracings of signals wherein
drawing A depicts essentially raw, unfiltered data (e.g., localized
neural stimulation pulses and remote-field cardiac activity
signals), drawing B depicts a filtered version of the data depicted
in drawing A, and drawing C depicts neurological stimulation being
delivered with a predetermined portion of the cardiac activity
(i.e., during myocardial repolarization, or T-wave, events).
DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS
[0022] Illustrative embodiments of the invention are described
below. In the interest of clarity, not all features of an actual
implementation are described in this specification. It will of
course be appreciated that in the development of any such actual
embodiment, numerous implementation-specific decisions must be made
to achieve the developers' specific goals, such as compliance with
system-related and business-related constraints, which will vary
from one implementation to another. Moreover, it will be
appreciated that such a development effort might be complex and
time-consuming, but would nevertheless be a routine undertaking for
those of ordinary skill in the art having the benefit of this
disclosure.
[0023] Illustrative embodiments of a method and apparatus for
providing improved cardiac function according to the present
invention are shown in the Figures. As will be readily apparent to
those skilled in the art upon a complete reading of the present
application, the present method and apparatus are applicable to a
variety of systems other than the embodiment illustrated
herein.
[0024] Generally, the instant invention is directed to a method and
apparatus for improving cardiac performance (e.g., hemodynamics)
and efficiency (e.g., balance between supply and demand and balance
within the neuro-endrocrinological systems) of the patient's heart.
In the illustrated embodiment, the current invention utilizes
electrical stimulation to treat ventricular dysfunction or heart
failure. As shown in FIGS. 1A and 1B, a system 100 may provide
Neural Stimulation Therapy (NST) (e.g. SCS, TENs, sub-cutaneous
stimulation, peripheral nerve stimulation) to a patient 102
adjacent one or more of the locations T1-T12, and C1-C8 or to
nerves on the chest, to improve cardiac performance and efficiency.
Such stimulation has been shown to stabilize cardiac electrical
activity, to reduce sympathetic activity of the cardiac tissue, to
improve the cardiac condition, and to reduce the likelihood of
ventricular arrhythmias. Thus, the electrical stimulation produces
effects similar to those induced by prescription beta-adrenergic
receptor blocking drugs. SCS has been shown to vasodilate
peripheral arterioles and increase blood flow to the limbs. SCS may
further cause the production of neuropeptides such as CGRP, NO, and
VIP that are known vasodilators, which may assist in redirection of
blood flow from regions of high flow to regions of low flow. This
further improves the performance and efficiency of the heart. In
the ischemic dilated cardiomyopathy patients, this therapy may
suppress or reduce sub-endocardial ischemia, and hence be
cardio-protective. Electrical stimulation may further result in
improvements in operational efficiency and function of cardiac
tissue even in the presence of reduced blood supply.
[0025] A controller 104 is coupled through conventional conductive
links 106, such as leads or wires, to one or more electrodes 108
mounted in a region adjacent the T1-T12 and C1-C8 vertebrae and
their associated nerve bundles. The electrodes 108 may take on any
of a variety of forms, including but not limited to conventional
surface mounted 1 electrodes, such as are commonly used in
conjunction with Transcutaneous Electrical Neurological Stimulator
(TENS) units. These surface mounted electrodes may be fixed to the
patient 102 via any of a variety of conventional mechanical or
chemical mechanisms or may be simply held in place by friction and
gravity. Alternatively, conventional implantable electrodes may be
surgically inserted into the spinal region adjacent the T1-T12 and
C1-C8 vertebrae, and may be located near or even immediately
adjacent the T1-T12 and C1-C8 nerve bundles for spinal cord
stimulation.
[0026] Implantable electrodes may be placed subcutaneously to
stimulate underlying muscles, overlying cutaneous nerves, or
passing somatic nerves. For example, lead Model 3987, is a
peripheral nerve stimulation lead available from Medtronic, Inc.
with four contacts and a polyester mesh skirt for fixation to
subcutaneous tissue or muscle fascia. Other Medtronic leads might
also be used, including Model 3587A or Model 3998, which have an
insulative paddle enlargement, or Model 3487A or Model 3888, which
do not. In both surface mounted and implanted electrodes,
electrical signals supplied by the controller 104 to the electrodes
108 electrically stimulate nervous tissue in the spinal canal,
sometimes by activating axons in nerves that connect to the spinal
cord
[0027] Implantable electrodes may be placed adjacent to nerves such
as the median, peroneal, ulnar, and ansa lenticularis nerves to
provide stimulation according to the current invention. Similarly,
implantable electrodes may be placed near the vagus nerves, carotid
sinus, and all other cranial nerves to provide stimulation.
Finally, implantable electrodes may be placed epicardially or
transvenously near the cardiac ganglia or plexi and also employed
in this manner.
[0028] The controller 104 may take the form of an external device
or an implantable device. Where the controller 104 is an external
device, it may be useful in providing therapeutic signals to a
patient who is experiencing an unexpected cardiac event, such as a
first or otherwise unanticipated episode of ventricular
dysfunction, heart failure, cardiovascular collapse, etc. However,
where the patient has a history of cardiac events, it may prove
useful to construct the controller 104 in a housing designed to be
implantable within the human body, such as is common in cardiac
pacemakers and defibrillators. The controller 104 may be programmed
for either automatic or manual operation. That is, the controller
104 may have one or more conventional sensors (not shown) of a type
capable of sensing a cardiac event or a precursor to a cardiac
event in the patient (e.g., a decompensation episode of ventricular
dysfunction, heart failure, and cardiovascular collapse). The
sensors and control scheme used to detect the cardiac event or a
precursor to a cardiac event may be conventional, such as is found
in implantable defibrillators or pacemakers. Upon detection of the
cardiac event, the controller 104 may automatically begin
therapeutic treatment of the patient by electrically stimulating
the T1-T12 spinal nerves or parts of the cervical or thoracic
spinal cord. Alternatively, a patient or authorized person may
manually activate the controller 104 to begin this therapeutic
treatment. Manual activation may be accomplished by any of a
variety of mechanisms. For example, where the controller 104 is
implanted in the patient, activation may be accomplished by
wireless communication or the like.
[0029] In those situations in which a patient has a history of
cardiac events, it is generally useful to construct the controller
104 in a housing 105 designed to be implantable within the human
body, as shown in FIG. 1B. In this embodiment, implanted lead 106
[change 106c to 106 in the drawing] is employed to deliver SCS
according to the invention.
[0030] The therapeutic treatment administered by the controller 104
may take on a variety of different forms. In one embodiment, NST
(e.g., SCS) delivery can be used to titrate the pressure-volume
relationship of the heart in conjunction with other types of
therapy, such as one or more types of pacing therapies. For
example, an adjustment of the atrio-ventricular (AV) and
ventricular-ventricular (V-V) timing during atrial-synchronized
bi-ventricular pacing (which is one form is known as cardiac
resynchronization therapy or CRT) can be performed at about the
same time as the NST delivery to further improve the performance
and efficiency of the heart.
[0031] Additionally, the stimulation therapy may be administered
along with cardiac resynchronization therapy to further improve the
cardiac performance and efficiency of the heart. That is, the SCS
or another NST (e.g. TENs, subcutaneous) therapy may be administer
shortly before, shortly after, or at the same time as
resynchronization or other pacing therapy. For example, the SCS
therapy can be administered in conjunction with bradycardia pacing
therapy, such as those causing changes in the lower rate limit
(LRL--atrial or ventricle); therapies for increasing cardiac output
or pulse pressure, such as post extra-systolic potentiation (PESP)
pacing or non-excitatory stimulation (NES) pacing; and/or therapies
for preventing arrhythmias or reducing arrhythmic burden, such
including arrhythmia prevention pacing algorithms, such as
consistent A or V pacing and rate stabilization pacing. In
particular, one exemplary scheme involves administering the
stimulation therapy in conjunction with overdrive RV apical pacing
to provide improved cardiac output for example in patients with
obstructive cardiomyophathies. In addition, the therapy may be
administered in conjunction with other device therapies to further
improve the cardiac performance and efficiency of the heart. These
device therapies may include, but are not limited to, drug delivery
device therapies, automatic external defibrillation therapies,
treatments provided by monitoring or diagnostic devices, and
therapies provided in conjunction with patient management and
information tools.
[0032] In one embodiment, delivery of the SCS therapy may be
modified based on a variety of measurable physiologic parameters.
As depicted in FIGS. 1A and 1B, representative sensors (not
depicted) may be positioned adjacent or within the body of the
patient 102 to sense various physiological conditions, which are
communicated back to the controller 104 over a conductive lead or
leads. The measured physiological conditions may be used as an
indication of the patient's response to the therapy being
administered by the controller 104. For example, a positive
physiological response may be used as an indication that the
therapy is achieving the desired result. The sensed physiological
conditions may be used to adjust the parameters of the SCS. For
example, the controller 104 may measure and record cardiac
pressure. A change in the cardiac pulse pressure may be used in a
closed-loop system to adjust delivery of SCS. For example, if the
controller 104 detects that the cardiac pulse pressure has declined
over time, then the parameters of the SCS may be adjusted in an
attempt to increase the cardiac pulse pressure. On the other hand,
where the controller 104 observes a consistent, appropriate cardiac
pulse pressure, then the stimulation delivered to the T1-T12 nerve
bundles may be continued, as a desired result is being achieved by
the SCS. On the other hand, where the controller 104 observes
continued high, or even rising, cardiac pulse pressure, then the
parameters of the NST may be adjusted in an attempt to lower the
cardiac pulse pressure over time.
[0033] Other parameters that may be measured and used as feedback
in a closed loop control system for NST delivery include, but are
not limited to, pressure-volume (PV) loops, pressure-area (PA)
loops, pressure-dimension (PD) loops, diastolic and systolic
pressures, estimated pulmonary artery pressure, change in cardiac
pulse pressure, pre-ejection timing intervals, heart rate measures
(such as, rates, intervals, and the like), autonomic indicators
(such as, heart rate variability, direct neural recordings, and the
like), chemical sensors (such as, catecholamines, O.sub.2
(saturated venous and/or arterial), pH, CO2, and the like), or
non-cardiac physiologic sensors (such as, activity, respiratory
rate, time of day, posture, and the like). Those skilled in the art
will appreciate that any of a wide variety of measurable
physiologic parameters may be monitored and used to implement the
closed-loop adaptive controller described herein. An exemplary
controller is described in greater detail in co-pending U.S. patent
application Ser. No. 10/035,319 entitled "Closed-Loop
Neuromodulation for Prevention and Treatment of Cardiac Conditions"
filed on 26 Oct. 2001, and the contents of which are entirely
incorporated herein by reference.
[0034] Any combination of the foregoing may be used to determine
the timing, waveforms, and amplitude of the electrical stimulation
delivered to the electrodes 108. Those skilled in the art will
appreciate that the illustrated, representative sensor may take on
any of a variety of forms, depending upon the physiological
parameter being sensed. Generally, these feedback parameters may be
detected and used to control certain parameters of the stimulation,
such as the magnitude, duration, duty cycle, and frequency.
Typically, the stimulation falls within the range of about 200-400
microsecond duration pulses, at a frequency in the range of about
50-100 Hz, and at a voltage of up to about 6V. For example, with
greater stimulation parameters (increased magnitude, increased
frequency, increased duty cycle, and/or increased pulse durations,
there is a potential for greater beta-blocker type (withdrawal of
sympathetic activity) effect. This would result in decreased
contractility, alteration in blood flow (increase in coronary
supply), improved cardioprotection and decreased workload or
demand. An additional example is the appropriate use of pre-set
parameters in response to sensed cardiac event information of the
patient. For example, if the patient is having a decompensation
ventricular dysfunction or heart failure event, then "more
strenuous" stimulation parameters (e.g. increased magnitude,
increased pulse width and increased frequency) may be used to
provide the greatest amount of protection and local withdrawal of
sympathetic activity. For a less severe event, such as an elevation
in end diastolic pressure, then "less strenuous" stimulation
parameters may be used to provide an incremental adjustment to the
cardiac function.
[0035] FIG. 2 illustrates a block diagram of one embodiment of the
controller 104. Generally, the controller 104 is comprised of one
or more driver circuits 200 and receiver circuits 202. The driver
circuits 200 are generally responsible for providing the
stimulating signals over the lines 106 to the electrodes 108. That
is, a processor 204, operating under software or hardware control,
may instruct the driver circuit 200 to produce a stimulating signal
having a set of preselected, desired parameters, such as frequency,
duty cycle, duration, waveform shape, amplitude, voltage and
magnitude. As noted above, driver circuits 200 may optionally
include circuits 201 [not shown] to generate high-voltage
defibrillation stimulation to the heart on leads 106 using
subcutaneous or other NST electrodes 108.
[0036] The receiver circuits 202 are generally responsible for
receiving signals from the optional one or more physiologic
sensors, and processing those signals into a form, such as a
digital format, which may be analyzed by the processor 204 and/or
stored in a memory 206, such as a dynamic random access memory
(DRAM). The memory 206 may also store software, which is used to
control the operation of the processor 204. Cardiac signals can be
filtered with a hardware filter or digitally, especially when the
sensing of cardiac signals is interfered with by the local
neurological stimulation therapy (as shown and described
hereinbelow in relation to FIG. 8).
[0037] In one embodiment, signals stored in memory 206 may be
transferred via a communication circuit 207 such as a telemetry
circuit to an external device 209 such as a programmer. These
signals may be stored in the external device, or transferred via a
network 211 to a remote system 213 which may be a repository or
some other remote database. Network 211 may be an intranet,
Internet system such as the world-wide web, or any other type of
communication link.
[0038] The overall general operation of the controller 104 may be
appreciated by reference to a flowchart depicted in FIG. 3. Those
skilled in the art will appreciate that the flowchart illustrated
herein may be used to represent either software that may be
executed by the processor 204 or hardware configured to operate to
perform the functions set forth in the flowchart. The process
depicted in FIG. 3 begins at block 300 with the assumption that a
cardiac event may have been detected either automatically or
manually, but in any event, therapy is being administered by the
controller 104.
[0039] At block 300, the processor 204 receives the measured
physiological parameters via the receiver circuits 202. At block
301, signal processor occurs to improve the signal to noise ratio
and remove spurious signals or the like. At block 302, the
processor 204 compares the measured parameters to corresponding
desired ranges. If the measure parameters are within the desired
range, as determined at block 304, the processor 204 returns to
block 300 and the process repeats. On the other hand, if the
measured parameters fall outside the desired range, then the
processor 204 at block 306 adjusts the stimulation parameter, which
should result in the physiological parameters of the patient being
adjusted to fall within the desired range. Then, in one form of the
invention, at decision step 308 the neurostimulation therapy is
optionally synchronized to the cardiac cycle. In the event that the
decision is affirmative then the method proceeds to block 310
wherein the neurostimulation therapy is adjusted to occur (or not
occur) during all or a part of the cardiac cycle. Thereafter, the
process returns to block 300 and the process begins anew.
[0040] It should be appreciated that, owing to physiological
differences between patients, an adjustment to the stimulation
parameters may not produce an immediate, precise change in all
patients. Rather, it is anticipated that each patient will respond
substantially uniquely to variations in the stimulation parameters.
Thus, it may be useful to add controllable variability to the
operation of the feedback arrangement described herein. For
example, it may be useful to control the rate at which the
stimulation parameters are allowed to change, or to develop a
histogram for a particular patient. The inventive system could
include the ability to record parameters associated with the
delivered NST such as pulse widths, frequencies, duty cycles, and
time varying patterns. These parameters and the patient's response
may be recorded in the memory 206, for example. Based on patient
response, the efficacy of the NST can be evaluated so that the
delivered NST can be adjusted to further improve cardiac
performance and efficiency. This "learning" capability allows the
system to optimize NST delivery based on prior patient data so that
treatment is automatically tailored to individual patient needs.
Furthermore, within a particular patient it may be useful for the
device to tailor its therapy based on prior learning. For example,
the onset or character of cardiac events may differ from episode to
episode. It may be useful for the system to recognize multiple
types of events (differing in, for example, severity, rate of
onset, time of day or occurrence, patient activity levels, etc.)
and treat these events with a uniquely tailored set of treatment
parameters. Again, the device memory may be used to record
parameters and patient responses to tailor treatments to different
patterns of parameters.
[0041] In an alternative embodiment, a combined neuro and pacing
stimulator Implantable Pulse Generator with outputs for neural
stimulation (e.g. SCS, TENs, sub-cutaneous, peripheral, etc.) is
provided. Lead attachments may be provided, in one instance, by a
PISCES QUAD-type lead commercially-available from Medtronic
Corporation, or an equivalent. Stimulation may be used in
conjunction with cardiac resynchronization or other pacing therapy
to improve cardiac function and may further be optimized based on
some diagnostic parameter such as pressure, impedance, volume, or
dimension, as discussed above. The Implantable Pulse Generator may
further include a drug delivery system so that drug therapy to
improve cardiac function may be automatically titrated with the
stimulation. The implantable pulse generator may further includes a
patient monitoring, diagnostic, or management system so that
diagnostic and patient information therapy to improve cardiac
function may be used in conjunction with neural stimulation.
[0042] In another embodiment, Spinal Cord Stimulation (SCS) may be
performed at cervical levels C1-C8 instead of, or in addition to,
T1-T12 stimulation. In yet another embodiment, Peripheral Nerve
Stimulation (PNS) may be performed at C2, C3, median, peroneal,
ulnar, ansa lenticularis, and/or dorsal root ganglia to improve
cardiac performance and efficiency.
[0043] In many of the above-described embodiments, the electrical
stimulation is described as SCS therapy, which may be delivered
using one or more implanted electrodes located adjacent the spine,
for example. However, it will be understood that stimulation using
externally-applied electrodes, or subcutaneous electrodes located
under the skin may also be used to obtain the benefits discussed
above. In the case of an externally-applied electrode system, a
portable stimulation device carried or worn externally by the
patient may be used to provide treatment. Moreover, in a general
form of the invention the neurological therapy comprises any
electrical stimulation and the site for the therapy delivery also
serves as the remote-sensing site for gathering cardiac activity
signals.
[0044] In one embodiment, a paddle-type (flat) lead having a
surface area between one square cm and five square inches or more
may be used to accomplish the subcutaneous stimulation. Such a lead
may be formed of an insulative material, with programmable
electrodes on one or more of the flat sides of the lead for either
skin stimulation, muscle stimulation, or both.
[0045] In one embodiment, electrodes may be provided on both sides
of the lead, with the electrodes employed for stimulation at a
given time being selectively enabled by a user. Alternatively, the
system may be programmable to select the type of tissue to be
stimulated. This is desirable since in some instances, it may be
beneficial to provide stimulation to only spinal neurons, whereas
in other instances it may be desirable to also stimulate skin
nerves, muscle nerves, peripheral nerves, cranial nerves, such as
the vagus, ganglia and plexi, or any combination of such nervous
tissue. Various electrode combinations could be provided to allow
for selectively enabling the stimulation in this manner.
[0046] In another embodiment, the paddle-type lead is between four
and ten millimeters wide to easily pass through a twelve-gage
needle before it unfolds. A special needle may be provided having
an oval or rectangular cross-section of appropriate size to allow
for the delivery of this type of lead. Electrodes may be provided
on one or both sides of the paddle lead. In yet another embodiment,
the electrodes of a cutaneous stimulation system could be placed on
the chest wall, or a stimulation source may be attached to leads
passed via needles to one or more subcutaneous sites.
Alternatively, electrodes may be placed on an outside surface of an
implanted pulse generator or pacing device or may be of the type
integrally formed with the can, shell, or housing of an implantable
device.
[0047] FIG. 4 is a flowchart illustrating one embodiment of the
current invention. A cardiac event such as ventricular dysfunction,
heart failure, or imbalance of autonomic tone or
neuro-endrocrinological system may be detected using measurable
parameters such as increased diastolic pressure, a lower heart rate
variability, increased catecholiamine levels, or a change in
naturetic peptide levels (400). If a cardiac event is detected, any
concomitant therapies are performed (402). If neural stimulation is
not on (404), it is activated (406). This therapy delivery may
involve use of artificial intelligence or other learning
capability, as discussed above. Monitoring continues to determine
whether the cardiac condition still exists (400). Returning to step
404, if neural stimulation is already on, stimulation parameters
may be adjusted using physiological signals that may be sensed by
one or more physiologic sensors, and monitoring continues with step
400.
[0048] In block 400, if a cardiac event has terminated, processing
continues to step 410, where it is determined whether stimulation
is on. If not, processing continues with monitoring step 400.
Otherwise, stimulation deactivation is initiated (412). This may
involve a hysteresis so that stimulation is terminated gradually
over a predetermined period of time.
[0049] FIG. 5 is a flowchart illustrating one embodiment of
concomitant therapy delivery that may be provided in conjunction
with neural stimulation. This therapy corresponds to that shown in
step 402 of FIG. 4. This type of therapy may involve pacing,
defibrillation, drug delivery, monitoring, and/or patient
management therapies, for example (500). If such a therapy is not
enabled, no action is taken (502). Otherwise, if the therapy is on
(504), therapy parameters may be adjusted (506). This may be
performed using sensed physiological parameters, for example. If
therapy is not enabled, this therapy is activated (508). Therapy
delivery may be based on the results of previously-delivered
therapy in the manner discussed above, as may be accomplished using
artificial intelligence capabilities, for example. In either event,
processing continues by comparing the cumulative effects of neural
stimulation and the other therapy delivery so that the therapy
delivery may be adjusted, if necessary (510). For example, delivery
of stimulation to nerve tissue could increase pacing thresholds
associated with a concomitant pacing therapy. As a result, the
pacing therapy may need to be adjusted. In another example,
delivery of stimulation according to the current invention may
reduce pulse pressure, whereas a bi-ventricular pacing regimen
increases the pulse pressure. It may be desirable to monitor this
interaction and adjust one or more therapies as needed. This step
is performed using information provided by the sensors, the neural
stimulation system, and the concomitant therapy system(s), as shown
in block 512.
[0050] Referring now to FIG. 6, the following figure shows a
schematic representation of a neurological stimulation lead 106 and
a device body 105. Cardiac electrical signals can be sensed with
(1) any combinations between electrodes 108 (labeled EO-E4 in FIG.
6) on a neurological lead 106 and/or on an surface portion (labeled
A,B in FIG. 6) of a housing for device 105, or the conductive
housing itself, and (2) with a hardware/digital filter(s) similar
to or different from existing cardiac rhythm management (CRM)
devices such as a pacemaker or implantable
cardioverter-defibrillator (ICD), as is known in the art. Sensing
electrodes 108 (EO-E4) are preferably located in an epidural space
(e.g., T1 and T3) and in particular can be used to enhance the
detection of posterior myocardial ischemia and infarction, while
sensing electrodes (or vectors) between lead electrodes and a
conductive portion (A,B) of the implanted device 105 are used to
record cardiac electrical signals similar to standard ECG
recordings. The invention can involve using a unmodified existing
neurological stimulation lead 106 and/or implements dedicated
cardiac sensing electrodes operatively coupled to an existing
neurological lead 106 and device 105. The configuration and number
of electrodes utilized can vary, for example, a pair of
neurological electrical leads each having eight discrete,
addressable electrodes can be used. Algorithms for ischemia
detection and other diagnostic features can be used to filter
signal artifacts generated by a device or by myopotentials and the
like. Additional filtering can also be applied.
[0051] In addition, the SCS electrodes 108 may be implanted
proximate, on, adjacent or within a portion of a spinal cord.
Alternatively the SCS electrodes may be subcutaneously placed near
the spinal cord, or cutaneously placed over a patient's skin near
the spine. The SCS electrodes may be electrically connected to a
controller or other components in the system through conductive
leads or wires. The SCS electrodes may also be capable of
bi-directional wireless communication with a controller or other
components in the system.
[0052] Also, a variety of optional electrodes may be included in
the system. Optional electrodes may be implanted, subcutaneously
placed [should this be distinguished from Reveal and how it might
wireless talk to a stimulator?], or externally located. Optional
electrodes may be adapted for performing a variety of functions,
and may be placed at any location suitable for performing their
intended functions. Optional electrodes may comprise, for example,
nerve stimulation electrodes mounted on vagus or other nerves,
muscle stimulation electrodes (spaced from any myocardial tissue),
electrodes on transcutaneous electrical nerve stimulation units,
etc. Optional electrodes may be electrically connected to
controller or other components in the system through conductive
leads or wires. Optional electrodes may also be capable of
bi-directional wireless communication with controller or other
components in the system. The primary and/or optional electrodes
can be used to deliver a high voltage defibrillation therapy
provided a potentially lethal arrhythmia can be discriminated from,
for example, a sinus tachycardia or the like.
[0053] For example, in one embodiment a single SCS electrode is
located on a distal portion of an SCS lead, more than four SCS
electrodes can be arranged in a linear fashion, or six SCS
electrodes can be arranged in a pattern (e.g., diamond, rectangle,
etc.). In one form of the invention up to eight SCS electrodes are
arranged in two substantially parallel lines. The SCS electrode
configurations are examples used for illustration purposes only and
are not meant to be limiting
[0054] A controller can operatively coupled within a housing
disposed in a fully-implanted location, subcutaneously placed or
externally located. The controller can of course be constructed of
a conductive housing. Optionally, any number of electrodes adapted
to sense cardiac electrical signals may be exposed on a portion of
an outer surface of the housing and electrically insulated from the
housing. The electrodes can be iteratively tested so that the pair
or plurality that produces the best sensing results can be
programmed for chronic use.
[0055] The processor controls the time periods during which sensing
of cardiac electrical signals may be performed. For example, the
processor can be programmed to sense cardiac activity only when SCS
therapy is not being delivered by any of the SCS electrodes.
Alternatively, the processor may suspend all spinal cord
stimulation to initiate sensing, and then resume SCS or other NST
therapy after cardiac sensing and/or detection is completed.
Alternatively, the processor can sense the QRS complex of cardiac
activity signals and deliver a pulse train (e.g., 100-200 ms) of
neurological stimulation during the refractory period so to avoid
the interference of cardiac sensing artifacts from neurological
stimulation. The processor can coordinate sensing functions with
the functions of any optional electrodes, physiologic sensors or
any other optional medical devices.
[0056] FIG. 7 is a temporal trace of cardiac activity signals 700
collected using SCS electrodes spaced from a canine heart and
clearly depicting the well-known QRS-T deflections of the
ventricular depolarization-repolarization sequences (denoted by
their respective letter in FIG. 7) of a plurality of cardiac cycles
702,704,706,708,710.
[0057] FIGS. 8A-C depict three temporal tracings of signals wherein
drawing A depicts essentially raw, unfiltered data 80 (e.g.,
localized neural stimulation pulses 81 and remote-field cardiac
activity signals), drawing B depicts a filtered version 82 of the
data depicted in drawing A (81), and drawing C depicts pulawa od
neurological stimulation 86 being delivered with a predetermined
portion of the cardiac activity (i.e., during myocardial
repolarization, or T-wave, events 88). These drawings provide just
one aspect of the notion of linking neurological stimulation to
certain parts or phases of cardiac activity and are in addition to
the basic premise of the invention; namely, remote monitoring of
cardiac activity using neurological electrodes spaced apart from
the heart (e.g., disposed in electrical communication with a
portion of the vagus nerve above the cardiac branch). In one form
of the invention the neurological therapy delivery is intended to
benefit the cardiovascular system of a patient, in other forms any
impact on the system might be deemed indirect (e.g., providing
neurological stimulation to treat epilepsy, obesity, depression, or
the like).
[0058] From the foregoing discussion, one skilled in the art will
appreciate that the current system and method for treating
ventricular dysfunction, heart failure, or imbalance of the
autonomic tone allows the treatment to be titrated using a single
dorsally-located SCS system or other NST system. The particular
embodiments disclosed and depicted herein are intended as
illustrative only, as the invention may be modified and practiced
in different but equivalent manners apparent to those skilled in
the art having the benefit of the teachings herein. Furthermore, no
limitations are intended to the details of construction or design
herein shown, other than as described in the claims below. It is
therefore evident that the particular embodiments disclosed above
may be altered or modified and all such variations are considered
within the scope and spirit of the invention. Accordingly, the
protection sought herein is as set forth in the claims below.
* * * * *